The invention relates to a method and system for operating a combustion engine brake especially in a heavy vehicle like a truck or a bus. The invention further relates to an engine control unit which is adapted for operating a combustion engine according to this method.
EP 1 281 841 discloses an engine compression release brake system and a method for operating the same in which an electronic control unit varies the braking power level of the brake system for an internal combustion engine in response to a signal generated by a sensor for sensing an operation condition like for example a vehicle load, speed, grade or brake pedal position. By controlling the amount of braking on the basis of the vehicle needs, especially a noise reduction shall be achieved.
It is desirable to further improve the accuracy or efficiency or reliability of a combustion engine brake and to provide a method and system for operating such a brake in an optimized manner.
It is also desirable to provide a method and system for operating a combustion engine brake by which a demanded brake torque can be delivered more accurately.
According to an aspect of the present invention, a method is provided for operating a combustion engine brake by means of at least one first operating parameter value which is selected in order to create a demanded brake torque value, comprising a step of detecting a brake torque value which is delivered by the combustion engine brake for braking the vehicle, and, if the amount of the difference between the demanded brake torque value and the delivered brake torque value exceeds a predetermined first limit value, the combustion engine brake is operated by means of at least one second operating parameter value which is selected or controlled in order to create a corrected brake torque value.
The second operating parameter can be an additional and/or an alternative operating parameter in relation to the first operating parameter, and/or it can be the same parameter as the first operating parameter but having another operating parameter value which e.g. is accordingly adjusted or selected or controlled.
The term “amount” of the difference is to be understood in this disclosure as the value without a sign, i.e. independently of a positive or a negative value of the difference.
According to another aspect of the present invention, a system is provided for operating a combustion engine brake comprising an engine control unit for conducting the above method.
One advantage of this solution is, that variations of the brake power due to variations e.g. of the ambient temperature, operating conditions, manufacturing tolerances etc. can be minimized or compensated. Furthermore, changes in the brake power which are caused for example by wear or degradation of certain components of the vehicle, especially of the combustion engine brake, can be compensated as well by the method and system according to the invention.
Another advantage of this solution is, that the method and system can be used as well to monitor operating parameters of the combustion engine brake and to detect faults or realize diagnostics in the related components of the combustion engine by evaluating variations or deviations of these parameters.